1. Field
The present disclosure relates to a method for producing a hexagonal boron nitride film by using a borazine oligomer as a precursor and a boron nitride film obtained thereby.
2. Description of the Related Art
Boron nitride (also referred to as BN hereinafter) is a material having a boron atom (atomic number 5) and a nitrogen atom (atomic number 7) bound to each other at a stoichiometric ratio of 1:1. Between the boron atom and the nitrogen atom bound to each other, a strong sp2 covalent bonding is formed. In addition, weak van der waals force is present between two layers of boron nitride. Due to the difference in interatomic distance and in distance between two layers of boron nitride depending on bonding structures and types, different structures, such as cubic-boron nitride (c-BN), hexagonal-boron nitride (h-BN) and wurtzite-boron nitride (w-BN), are present.
Among those, hexagonal boron nitride (white graphene, h-BN) film is an insulator and is transparent and flexible. Basically, it is stable at high temperature, has thermal properties characterized by high heat conductivity, and shows mechanical properties, including a low elastic modulus and heat expansion coefficient, and high heat resistance and thermal shock resistance. In addition, such a hexagonal boron nitride film has a low dielectric constant and dielectric loss and shows a band gap of about 5.5-6.06 eV, thereby providing characteristics as a dielectric material. Meanwhile, it has a hexagonal structure, which is the same as the structure of graphene, a two-dimensional material having excellent physical properties and shows a lattice mismatch of merely about 1.7%, and thus may form various structures together with graphene. Therefore, by virtue of the excellent thermal properties, mechanical properties, electrical properties and structural characteristics as described above, a hexagonal BN film may be used for various industrial fields, and may be utilized particularly as a next-generation electronic material.
There are several methods for producing a hexagonal boron nitride film. Typical methods include a mechanical method, chemical exfoliation of bulk flake, vapor deposition using sputtering, ion implantation, atomic layer deposition (ALD), or the like. Particularly, chemical vapor deposition (CVD) method is used most frequently.
The mechanical method includes exfoliation of at least two layers of hexagonal boron nitride using Scotch tape. Upon exfoliation, weal van der waals force exists between two layers of boron nitride. Thus, the mechanical method is problematic in that it is limited in size of the exfoliated hexagonal boron nitride and in productivity.
The chemical exfoliation of bulk flake includes exfoliating bulk flake of hexagonal boron nitride by way of sonication in the presence of a solvent, such as dimethyl formamide and dichloroethane. The hexagonal boron nitride exfoliated by the chemical exfoliation has problems of its limited size and thickness control.
The CVD method includes gasifying borazine to allow its flow, decomposing borazine into boron and nitrogen at high temperature and allowing the reaction of boron and nitrogen on the surface of a specific metal catalyst substrate to form a hexagonal boron nitride film. The hexagonal boron nitride film obtained by the CVD method has low defects. However, the CVD method is problematic in that the film thus obtained has a different number of layers due to the difference in growth rate, an expensive gas controller or vacuum system is required, and gases showing a difficulty in handling are used.